The Alden's neighbor, Lina, thinks there's treasure hidden in her attic and she wants the Boxcar Children to help her find it. Of course, the children are eager to help search—but it appears they aren't the only ones looking for the treasure.

While staying at the Crooked House, the family home of their housekeeper Mrs. McGregor, the Aldens try to solve a riddle that will lead them to a hidden treasure.

When the Alden children go camping on Blizzard Mountain, a place said to be inhabited by a ghost looking for buried treasure, they begin to think someone or something is trying to scare them off.

The Aldens accompany their grandfather to his class reunion and investigate the possibility of a buried Civil War treasure, and of a ghost in the bell tower, at Goldwin University.

When the Alden family climbs to the top of Old Flat Top Mountain, they encounter a mysterious mountain cave, a perilous rockslide, and a secret treasure.